Evidence that recurrent Plasmodium falciparum infection is caused by recrudescence of resistant parasites.

Isolates of Plasmodium falciparum obtained from 12 children attending different health facilities in the Madang Province, Papua New Guinea were typed for allelic variants of merozoite surface protein-1 and merozoite surface protein-2. Blood was obtained just before treatment with either amodiaquine or chloroquine and at intervals following treatment. All patients examined were found to be infected with genetically different parasites. Nine of the children were found to have single infections while three had mixed infections. In all patients, parasites reappearing in the blood following treatment had the same genotype as parasites in the primary infection. These results indicate that parasites reappearing in the blood following treatment were the result of true recrudescence and not new infections.